Method and apparatus for lifting loads step-by-step, especially heavy loads

ABSTRACT

A stepwise lifting device has at least one profiled beam having two opposing side walls with an open channel therebetween, and a conventional lifting jack is accommodated in the channel and has a base portion and an extendable lifting portion with a thrust head attached thereto. Uniformly spaced along the side walls of the profiled beam are grooves, the top and bottom surfaces of which slope upwardly. First and second jack supporting elements are provided for insertion between the grooves during a jack lifting and lowering operation, the arrangement being such that the weight of the jack is taken alternately on said elements during upward and downward stepping of the jacks. Means are also provided for moving the supporting elements into and out of successive grooves as the lift ascends or descends.

United States Patent [191 Johansson May 6,1975

[ METHOD AND APPARATUS FOR LIFTING LOADS STEP-BY-STEP, ESPECIALLY HEAVY LOADS [7 6] Inventor: Dag Valdemar Henry Johansson,

Brevlada 8033, S-541 00 Skovde, Sweden 22 Filed: Apr. 27, 1973 [21] Appl. No.: 354,936

[30] Foreign Application Priority Data Primary ExaminerAl Lawrence Smith Assistant ExaminerRobert C. Watson Attorney, Agent, or FirmAnthony A. OBrien [5 7] ABSTRACT A stepwise lifting device has at least one profiled beam having two opposing side walls with an open channel therebetween, and a conventional lifting jack is accommodated in the channel and has a base por tion and an extendable lifting portion with a thrust head attached thereto. Uniformly spaced along the side walls of the profiled beam are grooves, the top and bottom surfaces of which slope upwardly. First and second jack supporting elements are provided for insertion between the grooves during a jack lifting and lowering operation, the arrangement being such that the weight of the jack is taken alternately on said elements during upward and downward stepping of the jacks. Means are also provided for moving the supporting elements into and out of successive grooves as the lift ascends or descends.

11 Claims, 9 Drawing Figures sum 10F 2 FHENTEDMAY SL975 .hu 1nlllnl METHOD AND APPARATUS FOR LIFTING LOADS STEP-BY-STEP, ESPECIALLY HEAVY LOADS For practical and economic reasons it is sometimes neither possible nor expedient to use a crane to lift a load. For example, the space around the object to be lifted may be too confined to permit the use of a crane. Or, the costs involved in moving a crane to the lifting site may be completely out of proportion with the job on hand, thereby rendering the use of a crane uneconomical. Occasionally the object to-be lifted may require the use of two or more cranes, thereby incurring additional costs. Furthermore, in some cases the object to be lifted cannot suitably be lifted by a crane.

It is known to the art to use so-called climbing jacks, which include a profiled beam, and a rack or similar device which a specially constructed jack engages in a manner such that the jack is moved up the beam while lifting the load. Jacks of this type however, are encumbered with serious disadvantages, the jacks must be of special construction, which makes them expensive, and the jacks cannot readily be adapted to different lifting conditions and loads. Furthermore, it is difficult when using jacks of known construction to manipulate the load to a desired position of alignment at a desired level. Also, in all known constructions, the jack is located outside the centre of the carrying structure, thereby subjecting the carrying structure to oblique loads.

The present invention relates to a device for lifting a load, especially a heavy load, step-by-step by means of at least one conventional jack, the device of the present invention affording considerable advantages over similar jacks known to the art and being much cheaper to manufacture than previously known devices of the type described.

The device of the present invention includes at least one jack having a base portion and an extendable and retractable lifting portion, at least one upstanding carrying structure, and first and second jack supporting means co-acting with said carrying structure to alternately support said base portion and said lifting portion during a load lifting and lowering sequence, said carrying structure having two opposing walls defining a jack receiving channel therebetween and having generally horizontal abutment surfaces being arranged on said opposing side walls for co-acting with said jack supporting means during said load lifting and lowering sequence in a manner such as to generally support the jack centrally within the confines of the carrying structure free from contact therewith.

So that the invention will be more readily understood and further features thereof made apparent, a number of embodiments of the device according to the invention will be described with reference to the accompanying drawings, in which FIG. 1 shows in perspective a device according to the invention in which four conventional jacks are embodied,

FIGS. 2a, 2b and 2c show, partly in section, three stages during a load lifting operation carried out by means of the device according to the embodiment of FIG. 1,

FIG. 3 is a sectional view of an element used with the device according to the invention, the section being taken through the line III-III in FIG. 2a,

FIG. 4 shows a slightly modified embodiment of the device according to the invention,

FIG. 5 is an enlarged partial view of the device according to the invention, seen from the side in FIG. 4,

FIG. 6 illustrates a further embodiment of the device according to the invention, and

FIG. 7 shows an embodiment where the carrying structure has a number of sections, one stacked on top of the other, and with which the second jack engaging means is formed by the section last stacked.

The main components of the device according to the embodiment of the invention shown in FIGS. 1-3 include one or more jacks 1 and a carrying structure 2 for each jack. The jacks 1 are of conventional construction and have a base portion 3 and a lifting portion 4 projecting therefrom, the lifting portion suitably carrying at its upper end a thrust head 5 having a larger diameter than the diameter of the lifting portion 4. The jacks are preferably hydraulically operated, although mechanical jacks may also be used.

The carrying structure 2 includes a profiled beam, preferably a U-beam, which is held in an upstanding position. The U-beam may be secured to a wall or other suitable supporting structure, which may be stationary or movable, but the manner in which the carrying structure 2 is secured does not form part of the present invention and will not therefore be described in detail.

There are disposed on the inner surfaces of flanged portions of the carrying structure 2 a number of grooves 6, the positions of the grooves being such that each groove in one flange is located opposite a corresponding groove in the other flange, so that the lower defining surfaces of the grooves in each pair are located in a common generally horizontal plane. The pairs of opposing grooves are disposed along the length of the carrying structure 2 in uniform spaced relationship and the distance between adjacent grooves is less than the length of stroke of the jack.

The opposing grooves 6 are desinged designed that their inner, mutually facing edge surfaces 25 are slightly higher than the back edge surfaces 26 of the grooves. Thus, as shown in FIG. 5, the abutment surfaces of the grooves slope slightly downwardly from the lip 25 of the groove to the back edge 26 thereof. Both the upper and the lower abutment surfaces of respective grooves slope in such a manner.

First and second jack supporting means 9, 10 are arranged to support the jacks 1 on the inside of the carrying structures, and are adapted to bear against the lower abutment surfaces of the grooves 6. Accordingly the ends of the supporting means are given a correspondingly inclined surface in which the edge surface 29 of the supporting elements is lower than a surface 30 located inwardly of said surface 29. Thus end surfaces of the supporting elements are formed to slope at the same angle and to the same extent as the abutment surfaces of the carrying structure 2. In this way, the supporting elements 9, 10 will hook into the grooves of the supporting structure, the firmness of this engagement increasing with increasing load. Any tendency for the grooved flanges of the carrying structure 2 to bow outwardly is effectively counteracted by the inclination of said surfaces 25 and 29 with respect to the axis of force of the load.

When a load is to be lifted by means of a device according to the invention, the requisite number of carrying structures 2, in this case four, are placed around the load which rests on one or more beams 7, the ends of which, in turn, rest on transversely positioned beams 8, the ends of the beams extending in between the flanges of a carrying structure 2. A supporting means 9 in the form of a supporting plate is inserted into opposing grooves 6 at a distance beneath the beams 8 sufficient for a jack 1 to be placed on the plate 9 with its head 5 beneath the co-acting end of the cross beam 8.

Hydraulic fluid under pressure is then fed to the jacks 1, which extends to lift the cross beam 8 to such an extent that the head 5 of the jack 1 and the load are raised slightly above a pair of opposing grooves 6 further up the carrying structure 2.

When this position is reached, the supply of hydraulic fluid is interrupted and a second supporting means, indicated by the reference numeral 10, which has the form of a plate of the same rectangular shape as plate 9 but with a U-shaped cut 1 1 arranged in its edge, is inserted into pair of opposing grooves 6 in a manner such that the lifting portion 4 of the jack beneath the head 5 is accommodated in the cut 11. When the jack 1 is then retracted, the beam 8 will be lowered and will rest on the supporting plate while further retraction of the jack 1 will cause the head 5 of the jack to hang on the supporting plate 10 and the base portion 3 of the jack to be lifted upward. When the base portion 3 is free from the lower supporting plate 9, the plate is withdrawn from the pair of opposing grooves 6, and when the base portion passes the next higher pair of opposing grooves, the plate 9 can be reinserted in those grooves and will again be in position beneath the base portion 3. When the jack is then extended, it will rest on the lower supporting plate 9 and its head 5 will be lifted from the upper supporting plate 10, which can then be drawn out of its grooves 6'. The lifting sequence is then repeated, the load thus being lifted step-by-step, by alternately extending and retracting the jack 1 and by moving the supporting plates 9, 10 up the carrying structure 2. To lower the load, the above described sequence of events is carried out in reverse.

FIG. 2a illustrates a stage in which extension of the jack 1 has just begun and the two supporting plates 9 and 10 are in position, FIG. 2b illustrates a stage in which the jack has been extended to the desired extent, only the lower supporting plate 9 being in position, and FIG. 2c illustrates a stage during retraction of the jack, only the upper supporting plate 10 being in position.

The positioning of the carrying structures 2 relative to the load and the way of supporting said structures is dependent on the circumstances and does not form part of the present invention. The problems associated therewith, however, should not present any problem to one of normal skill in the art.

FIG. 4 shows a further development of the device shown in FIGS. 1-3. It also includes a jack 1 and a carrying structure 2 provided with grooves 6. The difference between the device of FIG. 4 and that of FIGS. 1-3, is that the former is provided with extensions on the jacks, which accommodate the supporting plates 9, 10 when the supporting plates are located outside the grooves 6, and which move the same together with the jack 1 up the carrying structure. A plate 12 is detachably secured to the bottom surface of the base portion 3 and to the top of the lifting portion 4 beneath the head 5 thereof, by means of screws 14 for example. The plate 12 is provided with a platelike extension 15 projecting outwardly between the flanges of the carrying structure 2 and the extensions 15 is provided with strips 16 of U-shaped cross section, the open channels of which oppose each other and are arranged in such spaced relationship that when the supporting plates 9 and 10 are withdrawn from the grooves 6, the plates slide in between the strips 16 and are supported thereby. For convenience, the supporting plates 9 and 10 may be provided with hand grips 17. Thus, the jack 1 carries the supporting plates 9 and 10 along during the stepwise lifting and lowering movements, which considerably simplifies the lifting operation, especially when working at great height, and also reduces the risk of accident through falling supporting elements.

In the embodiment shown in FIG. 6, the supporting means 9' and 10' are detachably connected to the base portion 3 and the head 5, the supporting means 9' being connected to the bottom surface of the base portion and the supporting means 10' being connected to the upper surface of the head.

Each supporting means 9', 10' includes a supporting plate 18, which is provided with a diametrically extending grooves. Two jaws l9 and 20 are arranged for movement in opposite directions in the groove to engage, in an outwardly projected position, the grooves 6 of the carrying structure and in a withdrawn position to be free from the grooves 6. The jaws 19, 20 are urged towards the outwardly projecting position by means of a resilient force, preferably the force exerted by springs 21, although a pressure medium may also be used for this purpose.

The surfaces of the jaws 19, 20 facing the grooves 6 disposed in the flanges of the carrying structure 2, have on their lower portions planar, sloping surfaces 22 which extend and outwardly and downwardly so that when the jaws are extended each surface rests against a co-acting upwardly inclined defining surface of the groove 6, to thereby support the base portion 3 of the jack and the head 5. The upper portion of the edges of the jaws are defined by an upwardly inclined surface 23 extending in towards the centre of the jacks, the surface 23 upon upward movement of the base portion 3 and the head 5 coming into abutment with the upper edge surface of the co-acting groove 6 and under a camming action therewith forces the jaws l9 and 20 inwardly against the action of the spring 21.

Thus, as the jack 1 is alternately extended and retracted, the jaws l9 and 20 of the supporting elements 9 and 10 of the base portion 3 and head 5 will engage in a groove 6 and be forced out thereof to engage in the next succeeding pair of opposing grooves. In this way, the jack 1 and the load can be moved step-by-step up the carrying structure 2 without it being necessary for the operator to remove and replace the supporting elements.

In lowering the load, the jaws are not automatically pressed inwardly by the aformentioned camming action, so each jaw is arranged to co-act with one or more hydraulic piston and cylinder devices 24, to which bydraulic fluid is fed at suitable times to move the coacting jaw out of engagement with a groove 6. These hydraulic devices are of known construction and will not therefore be described or shown in detail.

The supporting means 9 and 10 are in the form of detachable units which may be mounted to conventional jacks.

With the embodiments described with reference to FIGS. 1-6, the carrying structure 2 has been assumed to be a unitary beam structure of finite height. Carrying structures of a fixed height may prove less useful with certain load lifting or load supporting operations, however, and to obviate any inconvenience in this respect the carrying structure used in the embodiment shown in FIG. 7 is composed of a number of stackable sections 2a, which can be placed one on top of the other to form a carrying structure of the desired height.

As will be seen from FIG. 7, each section 2a has arranged in opposing side wall surfaces thereof a groove 6", each groove preferably presenting upper and lower abutment surfaces which slope upwardly towards the opposing groove on the opposite side wall surface. The position of each groove 6" in respective sections 2a in such that the distance between adjacent grooves of stacked sections is shorter than the working stroke of the lifting portion 4 of the jack 1.

As in the embodiments of FIG. l-6, the grooves 6" of the embodiment shown in FIG. 7 are arranged to receive jack supporting means having groove engaging surfaces corresponding to the surfaces of the grooves. In the embodiment of FIG. 7, however, the grooves are intended only to receive the supporting means arranged to co-act with the base portion of the jack, while the jack supporting means arranged to co-act with the lifting portion 4 of the jack is the section 2a added to the stack of sections to extend the carrying structure. Thus, in this embodiment, the part of the lifting portion 4 engaging the load is detachably secured to it, by a nut and bolt 31 for example or by any other appropriate means, so that the jack is held suspended thereby on the top of the uppermost section 2a when the lifting portion 4 is retracted. The section 2a thus forms the supporting means for the lifting portion 4.

When using the embodiment illustrated in FIG. 7, two sections 2a are placed one on top of the other and locked together by means of a bolt, quick-release pin or other appropriate securing means (not shown). A jack supporting means 9" for co-action with the base portion of a jack during a load lifting and lowering sequence is placed in the lowermost grooves 6" and a jack 1 is placed on said means to be supported thereby within the confines of the carrying structure sections. The lifting portion 4 of the jack 1 is then extended for the part 30 to bear against the load 7 to be raised. The load is then lifted through a distance corresponding at least to the height of a section 2a and a further section 2a is placed on top of the uppermost section and se- :ured thereto. The lifting portion of the jack is then retracted, with the jack held suspended from the part 30 resting on the top surface of the further section 2a. Further retraction of the lifting portion 4 will cause the Jase portion of the jack to be lifted up through the sec- :ions, at least to a position where the jack supporting neans 9" can be moved to the next higher groove pair 5". The jack is then lowered onto the supporting means 9" and the sequence of events repeated until the carryng structure has reached the desired height.

The advantages afforded by this latter embodiment )ver known lifting and jacking devices will be apparent ;0 all skilled in this art and need not be recounted here. #"or example, in addition to lifting and lowering loads, :he device according to FIG. 7 may also be used to irive piles or the like into the ground beneath existing )uilding structures and to move heavy loads horizonally.

The invention, however, is not restricted to the described and illustrated embodiments, but can be modified within the scope of the following claims.

What I claim is:

1. A device for lifting loads in stages comprising at least one jack having a base portion and an extendable and retractable lifting portion,

a carrying structure for said jack having two opposing side walls spaced from each other and defining a jack receiving channel therebetween, said side walls having inside surfaces,

first and second jack supporting means each extending across the channel between the opposing side walls to alternately support said base portion and said lifting portion of said jack respectively, and

a plurality of generally horizontal abutment surfaces disposed in the opposing side walls and spaced along the length of said carrying structure,

said plurality of abutment surfaces being inclined downwards from the inside surfaces in the opposing side walls,

portions of said jack supporting means selectively engaging and co-acting with said abutment surfaces in the opposing side walls and having an equivalent chamfer to match said inclined abutment surfaces to support said jack centrally within the jack receiving channel of said carrying structure and free from contact therewith.

2. A device for lifting loads as claimed in claim 1 wherein said carrying structure is a U-beam with a length at least equal to the distance the load is to be lifted, and

said opposing side walls of said carrying structure include oppositely located horizontal grooves, the lower surfaces of which form said generally horizontal abutment surfaces.

3. A device for lifting loads as claimed in claim 2 wherein said first and second jack supporting means have the form of plates, capable of being inserted into and retracted from said grooves to alternately support said base portion and said lifting portion of said jack during load lifting and lowering sequences.

4. A device for lifting loads as claimed in claim 3 wherein said lifting portion of said jack has a head portion,

and

the second jack supporting plate has a notch accommodating said lifting portion so that said second jack supporting plate may support said lifting portion by supporting said head portion.

5. A device for lifting loads as claimed in claim 3, wherein holders are attached to the base portions and lifting portions of said jack to receive said first and second supporting means when they are retracted from the grooves in said U-beam.

6. A device for lifting loads as claimed in claim 2, wherein at least one of said first and second jack supporting means is detachably fastened to its jack and has two jaws which move outwardly in opposite directions to engage said grooves in said sidewalls to support said jack, and each jaw is biased toward an outwardly projecting position by a spring.

7. A device for lifting loads as claimed in claim 6, wherein a hydraulically operated piston and cylinder device is arranged to oppose the bias of the springs in said jaws to retract said jaws.

8. A device for lifting loads as claimed in claim 6, wherein each jaw includes a generally horizontal lower surface to act as a supporting surface for said jaw, and each jaw further includes a canted, inwardly sloping upper surface to co-act with the upper edge of said grooves to force said jaw inward during an upward movement of said jack supporting means.

9. A device for lifting loads comprising at least one jack having a base portion and an extendable and retractable lifting portion;

a carrying structure for said jack having two opposing side walls defining a jack receiving channel therebetween;

first and second jack supporting means to alternately support said base portion and said lifting portion of said jack respectively; and

a plurality of generally horizontal abutment surfaces disposed in the opposing side walls of said carrying structure receiving said jack supporting means and cooperating therewith to support said jack centrally within the jack receiving channel of said carrying structure and free from contact therewith;

said carrying structure being a U-beam with a length at least equal to the distance the load is to be lifted;

said opposing side walls of said carrying structure including oppositely located horizontal grooves, the lower surfaces of which form said generally horizontal abutment surfaces;

said first and second jack supporting means having the form of plates, capable of being inserted into and retracted from said grooves to alternately support said base portion and said lifting portion of said jack during load lifting and lowering sequences;

said opposing side walls having inside surfaces;

said abutment surfaces in said side walls of said carrying structure being inclined downward from the inside surfaces of the side walls; and

the portions of said jack supporting means co-acting with said abutment surfaces having an equivalent chamfer to match said inclined abutment surfaces.

10. A device for lifting loads in stages comprising at least one jack having a base portion and an extendable and retractable lifting portion,

a carrying structure for said jack having opposing side walls defining a jack receiving channel therebetween;

a first jack supporting means in the form of a plate to support said base portion in said carrying structure and a second jack supporting means for supporting said lifting portion in said carrying structure, said second jack supporting means being formed by a head member of said lifting portion;

said carrying structure comprising a number of U- shaped sections having opposing side walls and being placeable one on top of another into a stack to form a U-beam structure, each section being of a length less than the possible length of extension of said jack;

each of said sections having on the inner surface of each of said opposing side walls a substantially horizontal groove, the groove on each wall being opposite the groove of the other wall;

opposite side edges of said first jack supporting means being insertable into said grooves in said side walls, the lower edges of said grooves being inclined downwards from the inner surfaces of said side walls to co-operate with corresponding chamfers on said opposite side edges; and

the top edge of the topmost of said U-shaped sections in said stack forming a substantially horizontal abutment surface for said head member of said lifting portion. 11. A method of lifting a load, step by step, by a jack having a base portion and an extendable and retractable lifting portion, and an upright jack carrying structure having opposite side walls spaced from each other and defining a jack receiving channel therebetween, said side walls including inside surfaces and being provided with a plurality of horizontal grooves spaced along the length of the carrying structure, each groove having a corresponding groove on the opposite side wall, the lower side surface of said groove inclining downwards from the inside surfaces of said side walls, said method comprising the steps of engaging portions of a first jack supporting means to the inclining side surfaces of a first pair of opposed grooves in said opposite side walls, the portions of said first jack supporting means having a chamfer corresponding to the inclining side surfaces of the first pair of grooves, centering said jack between and spaced from the opposite side walls such that said jack is supported from its base portion on said first jack supporting means engaged to the first pair of grooves,

extending the lifting portion of the jack to raise a load on the lifting portion thereof, engaging portions of a second jack supporting means to the inclining side surfaces of a second pair of opposed grooves in said opposite side walls and above said first pair, the portions of said second jack supporting means having a chamfer corresponding to the inclining side surfaces of the second pair of grooves, and said second jack supporting means being constructed to engage said lifting portion of said jack, retracting the jack so that said lifting portion of said jack rests on said second jack supporting means,

continuing the retraction of the jack so that the jack is suspended from the portions of said second jack supporting means engaged to the inclining side surfaces of said second pair of opposed grooves and said base portion is lifted away from said first jack supporting means while the load is still on the lifting portion of said jack, and

re-engaging the portion of said first jack supporting means to the inclining side surfaces of a third pair of grooves in said opposite side walls and the third pair being intermediate the first and second pairs of opposed grooves so that upon renewed extension of the jack the base portion of the jack will be supported by said first jack supporting means whereby the centered jack and the load on said jack is lifted step by step relative to said carrying structure without adversely affecting the centered jack and the load thereon. 

1. A device for lifting loads in stages comprising at least one jack having a base portion and an extendable and retractable lifting portion, a carrying structure for said jack having two opposing side walls spaced from each other and defining a jack receiving channel therebetween, said side walls having inside surfaces, first and second jack supporting means each extending across the channel between the opposing side walls to alternately support said base portion and said lifting portion of said jack respectively, and a plurality of generally horizontal abutment surfaces disposed in the opposing side walls and spaced along the length of said carrying structure, said plurality of abutment surfaces being inclined downwards from the inside surfaces in the opposing side walls, portions of said jack supporting means selectively engaging and co-acting with said abutment surfaces in the opposing side walls and having an equivalent chamfer to match said inclined abutment surfaces to suPport said jack centrally within the jack receiving channel of said carrying structure and free from contact therewith.
 2. A device for lifting loads as claimed in claim 1 wherein said carrying structure is a U-beam with a length at least equal to the distance the load is to be lifted, and said opposing side walls of said carrying structure include oppositely located horizontal grooves, the lower surfaces of which form said generally horizontal abutment surfaces.
 3. A device for lifting loads as claimed in claim 2 wherein said first and second jack supporting means have the form of plates, capable of being inserted into and retracted from said grooves to alternately support said base portion and said lifting portion of said jack during load lifting and lowering sequences.
 4. A device for lifting loads as claimed in claim 3 wherein said lifting portion of said jack has a head portion, and the second jack supporting plate has a notch accommodating said lifting portion so that said second jack supporting plate may support said lifting portion by supporting said head portion.
 5. A device for lifting loads as claimed in claim 3, wherein holders are attached to the base portions and lifting portions of said jack to receive said first and second supporting means when they are retracted from the grooves in said U-beam.
 6. A device for lifting loads as claimed in claim 2, wherein at least one of said first and second jack supporting means is detachably fastened to its jack and has two jaws which move outwardly in opposite directions to engage said grooves in said side walls to support said jack, and each jaw is biased toward an outwardly projecting position by a spring.
 7. A device for lifting loads as claimed in claim 6, wherein a hydraulically operated piston and cylinder device is arranged to oppose the bias of the springs in said jaws to retract said jaws.
 8. A device for lifting loads as claimed in claim 6, wherein each jaw includes a generally horizontal lower surface to act as a supporting surface for said jaw, and each jaw further includes a canted, inwardly sloping upper surface to co-act with the upper edge of said grooves to force said jaw inward during an upward movement of said jack supporting means.
 9. A device for lifting loads comprising at least one jack having a base portion and an extendable and retractable lifting portion; a carrying structure for said jack having two opposing side walls defining a jack receiving channel therebetween; first and second jack supporting means to alternately support said base portion and said lifting portion of said jack respectively; and a plurality of generally horizontal abutment surfaces disposed in the opposing side walls of said carrying structure receiving said jack supporting means and cooperating therewith to support said jack centrally within the jack receiving channel of said carrying structure and free from contact therewith; said carrying structure being a U-beam with a length at least equal to the distance the load is to be lifted; said opposing side walls of said carrying structure including oppositely located horizontal grooves, the lower surfaces of which form said generally horizontal abutment surfaces; said first and second jack supporting means having the form of plates, capable of being inserted into and retracted from said grooves to alternately support said base portion and said lifting portion of said jack during load lifting and lowering sequences; said opposing side walls having inside surfaces; said abutment surfaces in said side walls of said carrying structure being inclined downward from the inside surfaces of the side walls; and the portions of said jack supporting means co-acting with said abutment surfaces having an equivalent chamfer to match said inclined abutment surfaces.
 10. A device for lifting loads in stages comprising at least one jack having a base portion and an extendable And retractable lifting portion, a carrying structure for said jack having opposing side walls defining a jack receiving channel therebetween; a first jack supporting means in the form of a plate to support said base portion in said carrying structure and a second jack supporting means for supporting said lifting portion in said carrying structure, said second jack supporting means being formed by a head member of said lifting portion; said carrying structure comprising a number of U-shaped sections having opposing side walls and being placeable one on top of another into a stack to form a U-beam structure, each section being of a length less than the possible length of extension of said jack; each of said sections having on the inner surface of each of said opposing side walls a substantially horizontal groove, the groove on each wall being opposite the groove of the other wall; opposite side edges of said first jack supporting means being insertable into said grooves in said side walls, the lower edges of said grooves being inclined downwards from the inner surfaces of said side walls to co-operate with corresponding chamfers on said opposite side edges; and the top edge of the topmost of said U-shaped sections in said stack forming a substantially horizontal abutment surface for said head member of said lifting portion.
 11. A method of lifting a load, step by step, by a jack having a base portion and an extendable and retractable lifting portion, and an upright jack carrying structure having opposite side walls spaced from each other and defining a jack receiving channel therebetween, said side walls including inside surfaces and being provided with a plurality of horizontal grooves spaced along the length of the carrying structure, each groove having a corresponding groove on the opposite side wall, the lower side surface of said groove inclining downwards from the inside surfaces of said side walls, said method comprising the steps of engaging portions of a first jack supporting means to the inclining side surfaces of a first pair of opposed grooves in said opposite side walls, the portions of said first jack supporting means having a chamfer corresponding to the inclining side surfaces of the first pair of grooves, centering said jack between and spaced from the opposite side walls such that said jack is supported from its base portion on said first jack supporting means engaged to the first pair of grooves, extending the lifting portion of the jack to raise a load on the lifting portion thereof, engaging portions of a second jack supporting means to the inclining side surfaces of a second pair of opposed grooves in said opposite side walls and above said first pair, the portions of said second jack supporting means having a chamfer corresponding to the inclining side surfaces of the second pair of grooves, and said second jack supporting means being constructed to engage said lifting portion of said jack, retracting the jack so that said lifting portion of said jack rests on said second jack supporting means, continuing the retraction of the jack so that the jack is suspended from the portions of said second jack supporting means engaged to the inclining side surfaces of said second pair of opposed grooves and said base portion is lifted away from said first jack supporting means while the load is still on the lifting portion of said jack, and re-engaging the portion of said first jack supporting means to the inclining side surfaces of a third pair of grooves in said opposite side walls and the third pair being intermediate the first and second pairs of opposed grooves so that upon renewed extension of the jack the base portion of the jack will be supported by said first jack supporting means whereby the centered jack and the load on said jack is lifted step by step relative to said carrying structure without adversely affecting the centered jack and the load thereon. 